Conventionally, a shearing type grinder for shearing and grinding plastic, wood, paper, metal, rubber, fiber, leather, or other solid objects has been known. For example, the shearing type grinder of this kind includes a shearing type grinder the present applicant filed previously (see Japanese Patent Laid-open Publication No. 8-323232).
As shown in a cross-sectional view of FIG. 11 illustrating a shearing type grinder, and in a C-C sectional view of FIG. 12, the conventional shearing type grinder 100 has a plurality of rotary blades 103 provided alternately across a spacer 104 in the axial direction of rotational axes 101, 102. The spacer 104 is formed in an outside diameter so that the base part of the rotary blades 103 may be positioned in the axial direction as shown in FIG. 11, so that the rotary blades 103 may be positioned in the axial direction and detachably mounted.
These rotary blades 103 are, as shown in FIG. 11, provided with a tool rest 106 detachably mounted on the rotational axes 101, 102, and a split type cutting blade 105 detachably mounted so as to surround the periphery of the tool rest 106. The rotary blades 103 are disposed in an overlapped state between mutually opposite sides of the rotary blades 103 rotating in the rotational direction R side, so that the mutual cutting blades 105 may be engaged with each other across a gap of, for example, 0.5 mm to 1 mm in the axial direction.
The cutting blades 105 provided on the outer circumference of the rotary blades 103 attract the workpiece to be ground 120, and grind the workpiece 120 by shearing actions between mutually opposite rotary blades 103.
Further, as shown in FIG. 13, an engagement step 107 is provided on the mounting surface of the cutting blades 105, and this engagement step 107 is engaged with an engagement protrusion 108 formed on the tool rest 106 so as to receive the grinding reaction. This split type cutting blade 105 includes a leading end edge 109 pointed in the rotational direction of a blade tip 127 projecting outward, and a side edge 110 (lateral edge) formed along the side outer periphery.
The leading end edge 109 and the side edge 110 are worn in an early stage due to shearing and grinding actions as shown in FIG. 14 (a), (b), but since the cutting blade 105 having the leading end edge 109 and the side edge 110 is formed in a split type, if the leading end edge 109 and the side edge 110 are worn out, only the cutting blade 105 can be replaced.
In the cutting blade 105 of the shearing type grinder 100 of this type, since the workpiece is attracted and ground by the leading end edge 109, and is sheared and ground by the leading end edge 109 and the side edge 110, the leading end edge 109 and the side edge 110 are worn early. The portion M shown in FIG. 14 (a), (b) is the worn portion.
An early wearing is a round wearing in the leading end edge 109 and the side edge 110, and this wearing causes the grinding performance to lower and the grinding efficiency to decline. Alternatively, depending on the workpiece, the leading end edge 109 and the side edge 110 may be cut off, and this defect may also cause the grinding performance and the grinding efficiency to lower.
Such wearing causes the grinding performance to lower and the grinding efficiency to decline because, as shown in FIG. 14 (b), the gap S1 between the side face and the side face of the mutually adjacent cutting blades 105 is extended to a double size of the worn portion M, and the workpiece drops in this widened gap S1, and passes through.
Therefore, if such wearing or defect (hereinafter called wearing loss) occurs, the cutting blade 105 is generally replaced with a new one.
However, even in the shearing type grinder 100 employing such split type cutting blade 105, for example, since scores of the cutting blades 105 are commonly used in one unit, it requires much cost and labor for replacement.
Moreover, the cutting blade 105 is manufactured of an expensive material entirely such as an alloy tool steel in order to enhance the wear resistance. In the case of the shearing type grinder 100 comprising many cutting blades 105 as mentioned above, an immense cost will be needed if attempting to replace the entire cutting blades 105 with new ones. It is also contrary to effective use of resources.